Need help fixing a Kohler shower faucet

This morning while I was showering, the lever on my Kohler faucet popped off while I was shutting off the water. From what I could tell, there's a simple screw that connects the lever to the post that turns the water valve. Problem is, the screw falls fairly easily back into the lever and doesn't stay rigid. So it doesn't seem like I can just turn the lever back onto the post. What's more, there's a toothed pattern on the lever that fits snugly onto the post, which has a matching male end. You can see everything from the photos in the gallery below (note I removed the "cylinder" spacer that covers things up).

I also noticed (and you'll see this in the photo) that there's a large screw in the inside of the lever (once I removed the cap) but I couldn't turn that at all and it wasn't clear to me how it would help to get the lever back on.

Any help with what I was hoping to be a simple task would be very much appreciated!!